//一、boolean、undefined、null
//boolean中true当作1、false当作false
// console.log(true +1);
// console.log(false+1)
//undefined 变量未赋值

//二、获取数据类型
//typeof
var num = 10;
console.log(typeof num);  //number

var str = "hello"
console.log(typeof str); //string

var flag = true;
console.log(typeof flag); //boolean

var un = undefined;
console.log(typeof un);  //undefined

var nul = null;
console.log(typeof nul);  //object

//prompt取过来的值是字符类型
var age = prompt("请输入你的年龄");
console.log(typeof age)



